Distillation of furfural



Sept. 23, 1952 J. A. BERRIMAN ET AL DISTILLA'IION OF' FURFURAL FiledJan. 5, 1949 Patented Sept. 23, 1952 fn; 't l !Ja'me's Chalmers `Selbie,Upminster, England-,1:`v

vassignorswto Shell Development Company, Sam

Francisco, Calif., a corporationlofiDelaware Applicatitn-January's,1949, serial Nesta-924# InKGreatgBrritain August 18,.1948- y* 1i A'Ihisiinvention rlates t'o improvements iniysolvent extraction! andrecovery systems. wherein the? -solvent'- is furfural. -v Moreparticularly, it is concerned with a'method of minimizing'corrosionofreduipmentandlossl of furfuralin a' solvent ex- 5 tractionofi-mixtures.pforganic'compounds utiliza-'L tractinprocessl: ffi i f .Li ingfurfuralY as selectivegsolvent.-v A further'.obff us'e offurfurala'sa'n extractive solvent for ject is -to`V minimizethe-corrosionzof :equipment` th Aseparation v'offmixtu'res of'organiccompounds utilized in such `extraction rprocesses, 'i including;isiwellknownand widely used,A both in liduidequipment utilized linz'the: recovery `of, theffurfs liquidand in vapor-liquid extractionprocesses. 10 fural Afor further use. Another object is to re- Thus, forexample; extraction with furfural is duce the loss of `furfural" in suchsolventextrae employed to`separa'te the" aromatiev and unsatutionprocesses.A .Otherxobjec'ts and-advantages rated components" from'-petroleum-l hydrocarbon Will; become 'apparent to thoseskilledfin:1theyartfv mixtures-ofthe lubrlcatingoil range" and sofimfronithe detailedrdescription of theiinventionwzzz prtvtheir oxidationand'viscositycharacters-.1 15 The exact nature of a1iof'thetausesf-ofthe; tics'f In such `processes the recovery of furfural developmentVof-corrosiveness in `furfural ,during assumes fas great anlmportance-asthe actual exuse in extraction processesv with their, accom.- tractionstep itself,'sinc'e normally the cost of the panyingvrecovery"operations for ithe furfuralrareIu'rfuralishigh--andfevensmall percentage-lossesY not fully known andunderstood at the present of-furfur'al-mayseriously affect the economy'of 20 time. However, there'isievidence which indicates the processas' awhle.-v vThev conventional method that some ofthe iuifuralV becomesvconverted tofy ofrecovering` furfural in those cases where the acidsand that Athis 'development-,fof acidityimay extracted materialhas ahigherv boiling point account for the corrosion problems whichV arise.`than fyfurfural isV to 'distill vthe furfural from' 25 and also to someextent for the 'lossrof furfuralfby thel extracted material. Thisdistillation nordecomposition," since thethermal decomposition mallytakesplace :in `the presenceof water; and of furfural is catalyzed .byacids. Whether; ornut` it is "therefore awfrfe'quent practicetoeffectthe the originof the'seundesirablefeaturesjisacdistillatinrecovery of'furfurallin--acolumn'procuratelyidentified in this way, a satisfactory duci'ng two streanisof furfural,adry streamf rein'edy'is not readily at handg. i* whichcan'be' returnedto -the extraction system 30v Neutral-mamn 'ofiany acidity. byConvent-,ibridi arid a'lwetstream from whih'the waterl phase has meanssuch" as the "addition of iacid neutralizing4 to beseparatel befr'e'gthefurfural is'returned compounds, for instanc'e'hydroxide's or carbon`V tovthe extraction step Vofjthesysteln-l -Alte'rna'-A ates f the alkalimetalsv or alkalineearth'metals, tively, however; thefurfural Ymay be''recovered in to the circulatingvfurfuraiisinadvisame; 'Inrthe a'SinglefStrcamffrQm-vvhivh the-vvat1"fphase is' 35 presente ofsuthtomptun'dsirfurai either 'poly-'- Sebalaltdvbflrjth?flfurl'lfvtuiflfl'S/"- the @XE merizes' Vor"-ur1`dei'g'os'-oth'er'auto-condensation trlCtin'S-Svtemf 'l y reactions such as theCannizzaro reaction'.VV Neu' ,Theuserof furffgrafl il? 5.1 1311'processs has hit??- tralization by means of weakerbases suchfasor-larto, Oftenbeen aCcQmpaflm by erctamfufldesu" yganic amines has beenproposed and' utilized with able features 'the mosn'lmpotmt Qwhvlchf. 40some successybut these,baseswill'themselvs rei-i ttt equipment tata itastma tt ttes@ mg/1th si??? 10559; ftlffml- @genital 1g products offurfural degradation. Moreover can e .salq a m emp Oymg Suchicopven 10p?thesedegradation'prodtttsiof furfurai intyitend- 45 neutralzfltlon.mehdS1a1-eXcsSSf 'theffld ttYV 'forni-coke which, if-allo'wedL-toaccumulate, neutrahzmg Compound are mevltable @mme Y could eventuallyblock various -parts ofthe equipat a' PH greater .than .7 fu1'fu1`9f1Polymerlzs ment such as heat exchanger and other tubes rapidly attemptstoneutr-ahze acdtyin circulatand distillation. clm'hs and. trays-I1'Since fuling furfural byisuch means often result' in some furaligexpengiv'e in'ffelationto the mixtures'run; 50T increase rather thandecrease in the furfural loss. dergoingextractio'and thereforecomparatively AA method has now been foundrwherebyany small furfurallosses mayalectdisproportionateacidity which may develop in solventextraction lythelcostoffthe process; and sincel plant; cor-`and'recovery systems employing furfural--as the ro'sion-'can alsovinifzol-vef'lie'av'yfcost iin f-r'eplace# solvent canbeeffectivelyineutralized;fand-any ments, maintenance vand shutdownQf'pla`,'r it-, it 55* losses'o-f furfuralthroughidecompositoniorfotherv1o claims.'V (orfana-4.715

becomes. az matter of considerable importancefto:

eliminateor'minimize these Aundesirablegfeaturesq lt'. is thereforeansobjectof-:this inventionto provide: an improvedrprocess'ifor.thegsolventex-Vv.

chemical conversion minimized without involving the objectionablefeatures already indicated.

According to the present invention a method is provided for minimizingcorrosion of equipment and loss of furfural in a solvent extraction andrecovery system wherein a mixture of organic compounds issubjec'ted toan extraction step by contact with furfural, and wherein furfural isrecovered from the extract by a distillation in the presence of waterand separation of a water. phase from wet furfural distillate or fromthe wet part of the distillate, which method comprises injecting an acidneutralizing agent which is an inorganic alkaline compound' andpreferably Yau alkali or alkaline earth metal basic compound or mixturesthereof, such as an oxide, hydroxide,

carbonate or bicarbonate of an alkali or Valkaline earth metal, into thesaid wet distillate orV the said Wet part of the distillate prior toYthe separation of a water phase therefrom, in such quantity :that theip'I-If Y'of Vthe .separated water tralizing agent. Injection'may becontinuous or.

by'means of periodic doses, but in either case it must be carefully'controlled so'that the pH of the water phase leaving the vessel in whichthe subsequent separation of the water and furiural phases takes placelies within the range specified above and preferably lies as close to pH'7 as possible. f

.Themerits of the present invention lie largely iny the'followingfeatures all of which tend to minimize any possibility of alkalicatalyzed reactions of 'furfural such as polymer formation or theCannizzaro reaction taking place:

(l) The acid neutralizing -agents now used are added,- at such a placein the system that they are in contact'wi-th the furfural for a minimumof timeff'" i y (2) The acid neutralizing'agents are added to thevfurfur-al where'it is coolest and are not present inV those parts of thesystem where the furfural is at a high temperature.

l .(3) `The acid neutralizing agents are added at a point where anyexcess of them and where the products of the neutralizing reaction areimmediately removed from the system in the separated water phase.

(4) In those systems wherein the furfural distillate consists of `twostreams,` a dry one and a wet one, the acid neutralizing agents areadded only tothe Wet stream with the result that only afraction of thecirculating furfural comes into contact with the acid neutralizingagents in each passage through the system.

v(5) The control yof the addition of the acid neutralizing agent isbased not on the acidity of thenfurfural inthe system 'but on theacidity of the water phase separating out from the wet distillate.AOwing to slightly incomplete'acid transfer from the furi'ural phase tothe water phase, the furiural phase is a little more acidic than theseparated water phase land consequently there is some sareguard againstexceeding a p-H 7 value for the returning furfural..

The invention may ,be illustrated by reference to the accompanyingdrawing, which is made a part of this specification, and which showsdiagrammatically one embodiment of the invention.

rihe drawing is a flow sheet of a plant for the solvent extraction ofpetroleum lubricating oil fractions wherein the aromatic and unsaturatedhydrocarbons are removed from the oil by means of extraction withfurfural and the furfural recovered from the extract by distillation andreturned Ytothe system.

The extraction system is represented by I I, wherein crude petroleumlubricating oil fractions are treated countercurrently with furfuralflowing from the furfural storage vessel I2. The exraction system may beof any conventional type and since the particular type employed is notrelevant to the invention this is not shown in detail. The resultingrainate which contains furfural is led by line I3 to a distillationcolurnn Ed, Where the bulk of the furfural content is removed bydistillation and returned by line I5 to he furfural storage vessel I2.The resulting partially stripped rainate then'ows through line it to-distillation column Il, where the last traces of iurfural are removedby steam stripping: The

finished raffinate, which is the desired product, cws from column I7 tostorage or to such other iinishing treatments as maybe necessary, andfthe distillate from column I'I, la mixture of waterV furiural, flows bymeans of line I9 into th reflux stream to distillation column 26.-

The extract phase from the extraction system I i, which consists offurfural and the undesirable aromatic and unsaturated bodies from `thecharge stock flows through line 2l and a suitable` heater (not shown) tothe distillation column 20 where furfural is distilled off together withanyv` Water present. The column'20 is so arranged that fur- Y furalreiiuxes and collects substantially dry on tray 'I from the bottom fromvwhere it flows, by means of line 22, to the furfural storage vessel I2.

Wet furfural passes from the top of column 28 to-` the `condenser 24 andthe -condensed mixture of furfural and water (condensed wet furfural)iiovvs to the separator 25 through line 26 into which line is fed acontinuous stream of a slurry of slaked lime (calcium hydroxide) inwater-(0.05 pound of slaked lime per gallon of water) from the dosingtank 21. The rate of flow of the slurry into line 25 is so controlledthat the pH of the water phase separating in and leaving the separator25 is within the range 5 to 7 and preferably as close to pH 7 aspossible. The furfural leaving the separator 25 flows through line 28and back` tothe top of column 2li.A The aqueous phase leaving theseparator 25 is treated for the recovery of the small percentage of thelfurfural it contains and when this furfural has been removed, :theWater passes to Waste. fIf desired a further cooler may be insertedbetween the condenser 24 and the separator 25, either before or afterthe point of mixture with the lime slurry. i

The extract solution which collects in the base of column 20 may now, ifdesired, via a heater toa pressure ash column 35 where further furfuralis removed which eventually flows to the furfural storage vessel I2 andthe extract from the foot ofv column 35 nov/s to the distillation column3| where the last traces of furfural are removed by steam stripping. Thedistillate from column 3I, a mixture of water and furfural, flows intothe reiiux stream to column 20.

When operating a process such as has been described above for everyhundred tons ofV furrural going into the extraction system only aboutauf 1140i;

period of time taken in passing through line 26 to separator 25; thiscontacting is effectedfwhile the condensed water and' furfural arestillin' an intimate'state of'mixing. Thus the danger ofA polymerization orother alkali catalyzed reactions taking placejis reduced to alminimum.

The followingfa'cts 'taken from actual plant operation illustrate, theimportant advantages accruing fromthe-practice of thepresent, invention.Wi th the aid of the Ytechnique ofthe present invention it has beenfound possible in rening to produce high viscosity index lubricating oilusing furfural as extractionsolvent, to extend A indelinivtely theperiod between plant stoppage duetogplant corrosion or plantobstructionby furfural degradation products. The average acidityj ofthe-'circulating furfural v'was reduced from about 0.09% (calculated asacetic acid) to about 0.003%fand'the loss of furfural was reduced from0.095% of the total furfural turnover to 0.03% of this same turnover, areduction in the loss of furfural of about 70% of the original loss whenthe process was practiced without the application of the presentinvention. y

Although the invention has been described above with particularreference to the solvent refining of mineral lubricating oils, it willbe readily understood that it is not so limited in its applications. Onthe contrary, it will be clear to those familiar with the art to whichthis invention pertains that the invention is applicableto any processwherein furfural is employed as an extractant and subsequently recoveredby distillation in the presence of water. This water may be presentowing to deliberate addition thereof to the system or by itsadventitious occurrence therein. The subsequent recovery of the furfuralfrom the extract by distillation in the presence of water may be appliedto extracts obtained in extractive distillations as well as inliquid-liquid solvent extractions as described already hereinbefore. Inthe case of extractive distillation, wherein the extracted material inthe extract is, for the most part, of a lower boiling point than thefurfural solvent, the extracted material is rst separated from thesolvent by distilling off said extracted material; but, then it isusually necessary from time to time, or substantially continuously froma sidestream portion of the recovered solvent, to separate the solventfrom accumulated higher boiling materials, including products ofdegradation and condensation or polymerization, often by a steamdistillation of the furfural from such higher boiling materials.

The following may be cited as further instances of specific processes towhich the invention is applicable: the use of furfural for theextraction of impurities from crude anthracene or anthraquinone; the useof furfural for the extraction of impurities, particularlynitrogen-containing impurities, from animal or vegetable oils or fats;the use of furfural for the puriiication of rosin; and the use offurfural for the separation of mixturesV of. glyceride oils of varyingdegrees of unsaturation.

We claim as our invention:

l. In a method for the recovery of furfural from mixtures of furfuralwith higher boiling organic compounds wherein the furfural is distilledin the presence of water from said organic compounds, the improvementwhich comprises: (l) distilling said mixture in a distillation zone inthe presence of water into an overhead produciaconsisting essentially ofvapors of water and iurw fural, a bottoms product containing saidhigher; boiling organic compounds with a reducedcori-w tent of furfuraland an intermediate product consisting essentially of substantially dryfurfural'.. and withdrawing the same from the distillationi zone; (2) atleast partially condensing the sepaj rated overhead vapor product afterwithdrawal from the 'distillation zone and injecting thereinto.

an inorganic alkaline compound as an acidic neu- A tralizing agent,prior to'stratiflcation of separate-, 1 water and furfural liquidphases,in such quark tity that the pH of subsequently resulting stratined waterphase is greater than five, but not: greater than seven; (3) stratifyingand immedir ately separating resulting liquid aqueous and'fur-V- furalphases; and (4) returning theseparated. furfuralfas condensate reflux tothe distillation zone. .l v.

Y 2. A method according` to claim l, wherein theacid neutralizing agentis an aqueous dispersion of an alkaline earth metal alkaline compound.

3. A method according to claim 1, wherein the acid neutralizing agent isan aqueous dispersion of an alkali metal alkaline compound.

4. In a method for the recovery of furfural from mixtures of furfuralwith higher boiling organic compounds resulting from the solventextraction of petroleum oil fractions by said furfural wherein thefurfural is separated by dlstillation in the presence of water from saidorganic compounds, the improvement which comprises: (l) distilling saidmixture in the presence -of water in an upright distilling zone whilemaintaining condensate reilux in at least an upper section of thedistilling zone, and producing an overhead vapor product consistingessentially of vapors of water and'furfural, a bottoms product'r whichis withdrawn therefrom containing the. organic compounds with a reducedcontent of urfural and a substantially dry liquid furfural condensate inan intermediate section of said distilling zone and withdrawing sametherefrom; (2) at least partially condensing the overhead vapor productafter Withdrawal from the distilling zone and injecting thereinto aninorganic alkaline compound as acid-neutralizing agent, prior tostratification of separate water and furfural liquid phases, in suchquantity that the pH of subsequently resulting stratied water phase isgreater than 5 but not greater than 7; (3) stratifying and immediatelyseparating resulting liquid aqueous and furfural phases; and (4)returning the separated furfural as condensate reflux to the uppersection of the distilling zone.

5. A method according to claim 4, wherein the mixture of organiccompounds constitutes an extract from a petroleum lubricating oilfraction.

6. A method according to claim 4, wherein the mixture of organiccompounds constitutes an extract from a petroleum lubricating oilfraction and the acid-neutralizing agent is an aqueous dispersion ofcalcium hydroxide.

'7. A method according to claim 4, wherein the acid-neutralizing agentis an aqueous dispersion of an alkaline earth metal alkaline compound.

8. A method according to claim 4, wherein the acid-neutralizing agent isan aqueous dispersion of an alkali metal alkaline compound.

9. In a method for the recovery of iurfural from mixtures of furfuralwith higher boiling organic compounds extracted by said furfural frompetroleum lubricating oil stocks wherein the furfural is separated bydistillation in the Wllifisiwthdrawnassuch. fronten intermediate:

pointlf seicl distilli'ngzone; i I 2) Lat leastpartlallyl.;cndensinglthe separated-overhead vaporproduct aftwithdrarwali .fromthe"distillation .zone .and u pud;gsiacidmeutralizing agent; prorto strati#eatini-ofllseparate f Water "andffurfural liquid. 's

phases, in such quantity that the pH of subse-:l quentlylstrtied''wa-ter phase is greaterrzthan 5 brt'not greaterY than -7; (3)-stratlfying and..

immediatelyseparatingf (resulting .liquid .arqueo-uss` 1 theinorganicalka-line compound Aacid-q;eutralizf-A REFERENCES ...orrED vTleiollowl'ngi. references are. vrof record' in they l'` VofJ-tlflispatent UNITEDSTTES PATENTS L

1. IN A METHOD FOR THE RECOVERY OF FURFUAL FROM MIXTURE OF FURFURAL WITHHIGHER BOILING ORGANIC COMPOUNDS WHEREIN THE FURFURAL IS DISTILLED INTHE PRESENCE OF WATER FROM SAID ORGANIC COMPOUNDS, THE IMPROVEMENT WHICHCOMPRISES: (1) DISTILLING SAID MIXTURE IN A DISTILLATION ZONE IN THEPRESENCE OF WATER INTO AN OVERHEAD PRODUCT CONSISTING ESSENTIALLY OFVAPORS OF WATER AND FURFURAL, A BOTTOMS PRODUCT CONTAINING SAID HIGHERBOILING ORGANIC COMPOUNDS WITH A REDUCED CONTENT OF FURFURAL AND ANINTERMEDIATE PRODUCT CONSISTING ESSENTIALLY OF SUBSTANTIALLY DRYFURFURAL, AND WITHDRAWING THE SAME FROM THE DISTILLATION ZONE; (2) ATLEAST PARTIALLY CONDENSING THE SEPARATED OVERHEAD VAPOR PRODUCT AFTERWITHDRAWAL FROM THE DISTILLATION ZONE AND INJECTING THEREINTO ANINORGANIC ALKALINE COMPOUND AS AN ACIDIC NEUTRALIZING AGENT, PRIOR TOSTRATIFICATION OF SEPARATE WATER AND FURFURAL LIQUID PHASES, IN SUCHQUANTITY THAT THE PH OF SUBSEQUENTLY RESULTING STRATIFIED WATER PHASE ISGREATER THAN FIVE BUT NOT GREATER THAN SEVEN; (3) STRATIFYING ANDIMMEDIATELY SEPARATING RESULTING LIQUID AQUEOUS AND FURFURAL PHASES; AND(4) RETURNING THE SEPARATED FURFURAL AS CONDENSATE REFLUX TO THEDISTILLATION ZONE.